参照

ヘルプ :help deoplete

CREATE SOURCE *deoplete-create-source*
To create source, you should read default sources implementation in
rplugin/python3/deoplete/source/*.py.
The files are automatically loaded and deoplete creates new Source class
object.
Source class must extend Base class in".base".
Note: The sources must becreated by Python3 language.
Note: If you call Vim functions in your source, it is not asynchronous.